Relay switching circuit



April 19, 1960 A. M. DIAMOND.ETAL

RELAY SWITCHING CIRCUIT Filed May 6, 1958 INPUT B+ I F163 .2 SPRING ADJUSTMENT INVENTORQ, ALLEN M. DIAMOND, JUfi/S KANBERGS, NEALE A. ZELLMER.

4 T TOR/VE Y.

United States Patent RELAY SWITCHING CIRCUIT Allen M. Diamond, Castro Valley, Juris Kanbergs, East Palo Alto, and Neale A. Zellmer, Belmont, Calili, assignors to the United States of America as represented by the Secretary of the Army Application May 6, 1958, Serial No. 733,461

1 Claim. (Cl. 317-1485) This invention relates to electrical switching systems employing electromagnetic switches.

in many applications, particularly in telephone systems and the like, there exists the need for an improved fastacting, electronisally-controlled electromagnetic switch. it is the object of this invention to provide such a switch.

in accordance with the invention, an electronic switch is constructed to include an electronic valve, such as a vacuum tube or transistor, a semiconductor diode capable of operating with a reverse potential greater than the Zener point on its characteristic, and a relay. Either a two coil polarized relay connected to produce bucking fields, or a single coil direct current relay with a bucking spring may be used. The output circuit of the electronic valve and a relay coil are supplied in parallel from a common direct current source which includes a load resistance. The diode is connected to be reversely biased and in series with the relay coil.

For a better understanding of the invention, together with other objects thereof, reference is made to the following description and to the accompanying drawings, in which like reference numerals denote identical elements, and in which Figures 1-3 are schematic circuit diagrams of embodiments of the invention.

Referring now to Figure 1, there is shown a common emitter NPN transistor amplifier 10, the collector of which is connected through a relay coil 12 and load resistor 14 to the positive terminal of a bias source 16. The negative terminal of the serum is connected to the emitter of the transistor which is grounded. A second relay coil 18 is connected through a Zener diode 20 between the collector side of load resistor 14 and ground. As connected, the relay coils are poled to exert opposite forces on the movable arm of relay 22. Variable resistor 24 is shown connected across relay coil 12.

Assume that no input voltage is applied to transistor and therefore that it is cut-off. In which case, the drop across load resistor 14 will be minimum and the net voltage applied to diode 20 suliicient to cause it to offer a minimum of resistance due to its operation in the Zener region. Then, substantially the total current (less collector cut-off current) flowing will flow through coil 18, causing the movable contact arm of the relay to assume the position shown by solid line. If, however, a forward bias, positive in this case, is applied to the base of transistor 10, the transistor will turn on and a substantial current will flow through coil 12. Because of the increased voltage drop across load resistor 14, voltage applied across diode 29 will drop below the Zener range and the resistance of the diode will rise sharply. This, in turn, will cause the current through coil 18 to drop. Accordingly, the predominant force will now be exercised by opposing coil 12 and the relay contact arm will assume the dotted line position. Due to the relatively steep characteristic of the diode below the Zener point, the drop in current through coil 18 will occur sharply to insure rapid and positive relay action. Variable resistor 24 is included to allow any desired adjustment between the forces exerted by relay coils 12 and 18.

Figure 2 differs from Figure l, in that the bias is applied to transistor 30 and relay coil 38 through relay coil 32. Similar to Figure 1, diode 40 is in series with the parallel energized relay coil 38; the bias is applied in a like manner through load resistor 34; the relay coils apply opposite forces to control the movable contact arm of relay 42; and relay coil 32 is shunted by variable re sistor 44.

Inasmuch as relay coil 32 is in series with the current paths through both the transistor collector circuit and relay coil 38, relay coil 32 is constantly energized and, if unopposed, its force will result in the relay contacts assuming the solid line position. It will be unopposed when transistor 3'.) is turned on, as in this state the added current through load resistor 34 will reduce the potential across diode 40 sufiiciently to cause its resistance to increase and coil 38 in series with diode 40 to be ineffective. When transistor 30 is turned off, the voltage across diode 40 rises, the diode resistance decreases, and the current through coil 38 increases. This results in coil 38 exerting an overcoming force on the moveable contact arm causing it to assume the dotted line position.

Figure 3 is a variation of Figure 2 in which the constant restraining force supplied by coil 32 in Figure 2 is now supplied by spring assembly 52. Otherwise, transistor 50, load resistor 54, switching relay coil 58, diode 69 and relay 62 are arranged as are their counterparts in Figure 2 and their operation is the same. Relay coil 58 is energized when the transistor is cut off to pull the moveable contact arm to the position shown by the solid line. When the transistor is turned on, diode 60 is pulled below its Zener point and its increased resistance causes the current through relay coil 58 to drop and the moveable contact arm to assume the dotted line position.

While there has been described what is at present considered a preferred embodiment of the invention, many changes may be made without departing from the true spirit and scope of the invention, as defined in the appended claim.

What is claimed is:

A relay switching circuit comprising an NPN transistor having a collector, a grounded emitter and a base electrode, means for applying an input signal between said base and emitter electrodes, an output circuit comprising a relay having first and second coils interconnected at respective ends by a semiconductor diode, the free end of said second coil connected to said collector, said relay including a moveable contact arm which is in a first position when said first coil is energized and in a second posi tion when said second coil is energized, a direct current source having its negative terminal connected to both ground and the free end of said first coil and its positive terminal connected in series through a load resistor to the junction of said second coil and said diode, a variable resistor connected across said second coil, said diode capable of operation with a reverse potential greater than its Zener voltage point and being poled to oppose current flow through said first coil, said contact arm being in said first posiiton when said transistor is at cut-off and the voltage drop across said load resistor is at minimum so that the voltage applied to said diode is within its Zener range whereby substantially the total current from said source will flow through said first coil, and said contact arm being in said second position when said transistor is placed on by the application of said input signal and the increased voltage drop across said load resistor causes the voltage applied across said diode to drop below its Zener range'wherehy substantially the total current from said transistor will flow through said second coil.

References Cited in the file of this patent 

